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    HornetQ JMS QueueRequestor Example
    
    
    
  
  
     JMS QueueRequestor Example

     This example shows you how to use a QueueRequestor with HornetQ.
     JMS is mainly used to send messages asynchronously so that the producer of a message is not waiting for the result of the message consumption.
        However, there are cases where it is necessary to have a synchronous behavior: the code sending a message requires a reply for this message
        before continuing its execution.

        A QueueRequestor facilitates this use case by providing a simple request/reply abstraction on top of JMS.
     The example consists in two classes:
     
         TextReverserService
         A JMS MessageListener which consumes text messages and sends replies containing the reversed text
         QueueRequestorExample
         A JMS Client which uses a QueueRequestor to send text requests to a queue and receive replies with the reversed text in a synchronous fashion
    

         
     Example step-by-step
     To run the example, simply type ./build.sh (or build.bat on windows) from this directory

     
        First we need to get an initial context so we can look-up the JMS connection factory from JNDI. This initial context will get it's properties from the client-jndi.properties file in the directory ../common/config
                   InitialContext initialContext = getContext();
        

        We look up the JMS queue from JNDI
                   Queue queue = (Queue)initialContext.lookup("/queue/exampleQueue");
        

        We look up JMS queue connection factory from JNDI
                   QueueConnectionFactory cf = (QueueConnectionFactory)initialContext.lookup("/ConnectionFactory");
        

        We create the TextReverserService which will consume messages from the queue
                    TextReverserService reverserService = new TextReverserService(cf, queue);
        
        
        We Create a JMS queue connection
                   connection = cf.createQueueConnection();
        
         
        We start the connection. In order for delivery to occur on any consumers or subscribers on a connection, the connection must be started
                   connection.start();
        
         
        We create a JMS queue session. The session is created as non transacted and will auto acknowledge messages (this is mandatory to use it to create a QueueRequestor)
                   QueueSession session = connection.createQueueSession(false, Session.AUTO_ACKNOWLEDGE);
        
        
        We create a JMS QueueRequestor using the session and the queue
                   QueueRequestor queueRequestor = new QueueRequestor(session, queue);
        

        We create a JMS text message to send as a request
                   TextMessage request = session.createTextMessage("Hello, World!");
        
   
        We use the queue requestor to send the request and block until a reply is received.

            Using the queue requestor simplify request/reply use case by abstracting boilerplate JMS code
            (creating a temporary queue, a consumer and a producer, setting the JMS ReplyTo header on the request, 
            sending the request with the producer, consuming the message from the consumer).
            All this code is replaced by a single call to QueueRequestor.request() method.
            
                   TextMessage reply = (TextMessage)queueRequestor.request(request);
        

        The reply's text contains the reverse of the request's text
                   System.out.println("Send request: " + request.getText());
           System.out.println("Received reply:" + reply.getText());
        

        We close the queue requestor to release all the JMS resources it created to provide request/reply mechanism
                   queueRequestor.close()
        

        We do the same for the text reverser service
                   reverserService.close()
        

        And finally, always remember to close your JMS connections and resources after use, in a finally block. Closing a JMS connection will automatically close all of its sessions, consumers, producer and browser objects

                   finally
           {
              if (initialContext != null)
              {
                initialContext.close();
              }
              if (connection != null)
              {
                 connection.close();
              }
           }